1. Field of the Invention
This invention relates to methods of cutting sheet material and has particular reference to methods of cutting sheet materials with a tacky layer on them.
2. Description of the Prior Art
In the manufacture of photopolymerizable letterpress printing plates, a continuous sheet of steel is produced having a tacky layer of photopolymerizable material on its surface. Typically the sheet would be 0.010 inch thick and the tacky layer could be up to 0.070 inch thick. The sheet cannot be readily handled until the tacky layer has been allowed to dry. Drying basically involves removing the solvents from the tacky layer to enable the layer to solidify. It is not possible to heat the tacky layer to too great a temperature because bubbles will form if a critical temperature is exceeded. Since it is advisable to continuously coat a long strip of material if a uniform thickness coating is to be produced, this means that a very long sheet of steel covered with a tacky layer is produced. Because of the drying problem mentioned above, it might be thought necessary to have an extremely long production line which could enable the tacky layer to dry sufficiently to enable the sheet to be guillotined into discrete lengths.
At reasonable production rates, however, it has been found that the length of line required is more than is practicably possible.
On deciding to cut the sheet material into discrete lengths prior to drying, an investigation was made and it was discovered that there are no known methods suitable for cutting sheet materials, particularly sheet metals, which have a thick tacky layer on the surface and in particular a tacky layer of constant thickness.